A pyrolyzer and method is provided for devolatizing coal and other volatile materials. The pyrolyzer has a pyrolyzer furnace housing having at least two screws laterally positioned adjacent and overlapping rotatably mounted within the furnace for moving volatile material through the pyrolyzer furnace housing. The screws have hollow drive shafts with a diverter inside for converging heated fluid to heat the volatile material moving through the pyrolyzer furnace housing. A combustion chamber combusts fuel to create heated exhaust gas for directing through the hollow drive shafts to heat the volatile material. The pyrolyzer furnace housing may have a double wall with a cavity between, capable of receiving heated fluid for further heating of volatile material moving through the pyrolyzer furnace housing.